Modern internal combustion engines are equipped with cooling systems to prevent overheating which can lead to mechanical failure of engine components. Typically, the cooling systems utilize either air or a liquid coolant to remove excess heat from the engine. However, significantly greater amounts of heat can be dissipated by utilizing a liquid type cooling system. And, since the thermal loading of internal combustion engines is ever increasing in particular as a result of supercharging, a liquid type cooling system is generally provided.
In liquid type cooling systems of internal combustion engines, cooling channels known as water jackets are provided in the cylinder block and/or the cylinder head that allow the coolant to flow through the cylinder head or the cylinder block in order to remove excess heat. The water jackets entail a complex structure that weakens the structure of the cylinder head or block, which experience high mechanical and thermal loads. Also, in a liquid type cooling systems the heat does not first need to be conducted to the surface in order to be dissipated, as is the case with the air type cooling systems. Instead, the heat is dissipated to a coolant, which is generally water provided with additives, in the interior of the cylinder head or block.
A liquid cooled internal combustion engine has a coolant circuit that removes excess heat produced within the engine. A pump is arranged in a feed line of the coolant circuit causing the coolant to circulate. The coolant then flows from the feed line into water jackets of a cylinder block and/or head. Heat is dissipated to the coolant from the interior of the cylinder block and/or head when the coolant flows through the water jackets. Once the coolant flows out of the water jackets thorough a discharge line, the coolant then flows into a heat exchanger where the heat is then extracted from the coolant. The coolant circuit is then completed by a return line which branches off the heat exchanger, after the heat has been extracted from the coolant, and then opens up back into the feed line, where the process starts again. The discharge and feed lines do need not to constitute lines in the physical sense but rather may be part of the water jacket, and formed integrally with the cylinder block and/or head, or they may consist of a coolant inlet housing or coolant outlet housing.
In the heat exchanger, heat is transferred from the liquid coolant to a mass of air flowing across the heat exchanger. To provide an adequate amount of air flow to the heat exchanger, and to assist with the heat transfer, in all operating states but particularly when the motor vehicle is stationary or at low vehicle speeds, the cooling systems of modern motor vehicle drives are increasingly being equipped with high powered fan motors which drive a fan impeller. The fan motors are generally electrical and preferably can be controlled in a continuously variable manner with different loads or rotational speeds.
Additional vehicle systems requiring heat may also be utilized to extract heat from the coolant downstream of the cylinder block and/or head, after it flows through the water jackets in the cylinder block and/or head. For example, a coolant operated heater will utilize the coolant heated in the water jackets of the cylinder block and/or head to heat the air supplied to the passenger compartment of the vehicle, further decreasing the temperature of the coolant.
The water jacket of the cylinder head is often connected to the water jacket of the cylinder block, wherein the head is supplied with coolant from the block and vice versa.
According to the prior art, the heat exchanger provided in the coolant circuit is configured for maximum loading, so that the amounts of heat generated can be dissipated under all operating conditions, in order to ensure the functional reliability of the liquid cooled internal combustion engine.
Nevertheless driving situations arise where the engine cooling system reaches its performance limit especially during acceleration or when traveling on mountain roads. Under these circumstances, the cooling system has to dissipate relatively large amounts of heat because of high loads, while at the same time having a low air mass flow across the heat exchanger. The air mass flow across the heat exchanger will be low in these circumstances because the vehicle traveling at low speeds.
Here, it is not necessarily the component temperature of the engine, or the component temperature of the cylinder head alone, that reaches critical values first. In fact, the coolant itself may overheat downstream of the cylinder head and require cooling even before the internal combustion engine overheats.
Against the background of that stated above, it is an object of the present invention to provide a liquid cooled internal combustion engine where the engine cooling system is optimized during driving conditions where the coolant temperature reaches critical temperatures prior to the engine or individual engine components reaching their critical temperatures.
It is a further object of the present invention to specify a method for operating a liquid cooled internal combustion engine where the coolant temperature reaches critical temperatures prior to the engine or individual engine components reaching their critical temperatures.